1. Field of the Invention
The invention relates to a deposition ring used in semiconductor wafer processing systems. More particularly, the invention relates to apparatus for limiting the rotation of a deposition ring relative to a substrate support chuck that is circumscribed by the deposition ring.
2. Description of the Background Art
In deposition processes, species from a source such as a target, a gas inlet manifold and the like may deposit on exposed internal chamber surfaces, including the chamber walls and hardware. Shields are available which are designed to intercept such species. One portion of such a shield is a deposition ring (also known as a waste ring) that generally circumscribes a substrate support such as an electrostatic chuck and is designed to prevent deposition upon the edges of the substrate support. A substrate support typically contains a radially extending, circumferential flange that supports the deposition ring proximate the edge of the substrate support surface that is designed to support a workpiece such as a semiconductor wafer.
Typically, a substrate support, although generally circular in plan form, has one edge that is flat. The flat edge, circular shape matches the shape of a typical semiconductor wafer. Such a flat edge is used to easily orient the wafer during processing. So that the deposition ring can circumscribe the substrate support, the deposition ring also contains a flat portion of its inner circumference such that the geometry of the deposition ring substantially matches the plan form of the substrate support.
The deposition ring inner circumference is slightly larger than the outer circumference of the chuck. Such a size differential is necessary to ensure that the different materials comprising the ring (typically stainless steel) and the substrate support (typically ceramic or dielectric) are permitted to freely expand and contract in response to the extreme temperatures produced in a semiconductor wafer processing system.
The deposition ring, during thermal cycling, slides about the substrate support, i.e., the deposition ring rotates about the substrate support. At room temperature, the rotation is typically 0.35 to 1.5 degrees. However, at 400 degrees Celsius, the rotation can exceed 3 degrees. As a result, the flat portion of the deposition ring inner circumference contacts the edge of the substrate support at the point where the flat edge meets the circular edge. As the temperature within the processing system cools, the deposition ring contracts at a rate faster than the substrate support. If cooled while the deposition ring is in the excessively rotated position, the ring produces substantial inwardly directed force (compressive force) at the circumferential contact points between the ring and the support. As a result, the ring becomes "stuck" and cannot be easily removed from the substrate support. Such compressive force can permanently damage the substrate support.
Therefore, a need exists in the art for apparatus that limits the rotation of the deposition ring with respect to a substrate support that is circumscribed by the ring.